Technical field
[0001] The invention is a device for monitoring a patient's vital signs. The patient's respiratory
and pulse rate is measured using a measuring mat with one or more built-in measuring
members. Each of these measuring members consists of a unique sensor which senses
the mechanical action of forces on the mat resulting from the patient's breathing
and pulse.
Technical background
[0002] Current art offers a great number of devices for monitoring a patient's vital signs.
These monitors are regularly used in many hospitals, primarily in intensive care units.
Thanks to modern technologies a patient doesn't have to be connected to a device by
any cables and there is no longer a necessity of a patient and hospital personnel
to cooperate for the successful monitoring of the patient's vital signs. These contactless
monitoring systems can also be used in aftercare departments or nursing homes.
[0003] Most of these modern, but no longer overly unique, devices are based on a similar
principle. The main component of the measuring device is a mat with one or more integrated
sensors. These sensors may be of different types. One of the types is a sensor which
senses changes in forces acting on the mat. Another method uses accelerometers measuring
the vibrations of the mattress platform in order to measure vital signs. It is also
possible to use, for example, piezoelectric sensors and also additional capacitive
sensors. The mat is located under the location where the patient is recumbent generally
under the mattress.
[0004] Many embodiments of mats are known, i.e. in patent application
WO 2010080794 the mat is filled with a fluid and a pressure sensor senses changes in pressure caused
by the patient's breath and pulse rate. The problem of the solution is the complexity
of manufacturing a special mat filled with fluid.
[0005] One interesting solution is an evaluation of vital signs on the basis of an analysis
of video signal. Some vital signs are calculated on the basis of the ratio of the
intensity of light of two different wavelengths reflected from the patient's skin.
Such a solution is described for example in patent application
WO 2013027027. But this method is not very accurate and it is also difficult to make a measurement
using this method under poor lighting conditions.
[0006] There are also known solutions where the measuring member is integrated in the mattress.
We can see such a solution for example in patent
US 7652581. One disadvantage may be the price of the mattress adapted for this purpose.
[0007] Strain gauges, the main role of which is evaluation of a patient's weight, may also
be used for the implementation of a measuring device. If they are correctly adapted
they can also record the vibrations caused by breathing and heartbeat. But highly
sensitive strain gauges are necessary for this method of measurement and they may
be prone to interference and can often react to ambient forces which are not a subject
of interest. We can see such a solution in patent No
US 7699784.
[0008] As a result of the drop in the purchasing price of piezoelectric sensors they are
used in many branches, from medical devices, uses in the army or for building security.
Piezoelectric sensors are used in medical devices, for example in plethysmography,
measuring of blood pressure, measuring tremors, the movement of a patient or measuring
the pulse rate. Piezoelectric sensors work on the principle that they react to deformation
by generating measurable electrical voltage. They can be used to measure force, flexion,
extension and other values. The problem is that a piezoelectric sensor reacts very
badly to low frequency changes such as respiratory frequency. We can find the use
of these piezoelectric sensors for contactless monitoring of vital signs in patent
US 6984207, for example.
[0009] Capacitive sensors are often a part of medical equipment, and their advantage is
that compared to piezoelectric sensors they are also sensitive to low frequency mechanical
changes which are result of applied forces. For this reason they have a wide range
of uses, from measuring the level of liquid, measuring position or measuring force,
which can be used to measure a patient's respiration, for example. The use of these
capacitive sensors is described for example in patent application
WO 2006131855.
[0010] Contactless measurement of a patient's vital signs may be performed using inductive
sensors that measure the bio-impedance of the patient, on the basis of which the patient's
physiological expressions are evaluated. Such an embodiment is given, for example,
in patent application
WO 2006129212
[0011] Further monitoring devices according to the state of the art are for instance described
in
WO00/05771A1.
[0012] A modern trend in medicine is lower intervention in the patient's daily activities
and so contactless measurement of the patient's vital signs is more attractive. Most
often the arrangement of the present measurement of vital signs is a mat consisting
of one or more types of sensors. The sensors are for example piezoelectric, pressure
or capacitive sensors. These sensors differ in terms of their ability to react to
mechanical changes resulting from the patient's vital signs. For example a piezoelectric
sensor is distinguished by the fact that it reacts well to dynamic changes which can
be caused for example by the patient's pulse. Capacitive sensors react well to slow
changes such as a patient's respiration. The problem given by making contactless equipment
for the measurement of a patient's vital signs is that the sensors must be sensitive
to even slight changes caused mainly by the breathing and pulse of the patient and
they must not be disrupted by ambient forces. This can be achieved through a combination
of different types of sensors but it leads to very expensive measuring devices.
Summary of invention
[0013] Mentioned problems are resolved by a device according to claim 1. This solution is
advantageous because only one type of a measuring element modified in this way is
used for the contactless monitoring of the patient's vital signs.
[0014] Application of a mechanical force on the cover caused by the patient's vital signs
results the deflection of a metal strip. The arrangement of the metal strip, cover
and supporting body is approximately symmetrical, which means that the same perpendicular
force can exert anywhere on the entire surface of the cover, and it is expressed as
the same deflection of the metal strip. In an advantageous embodiment the measuring
member includes a flexible member which exerts a mechanical force on the piezoelectric
sensor via in the direction to the metal strip. An alternative embodiment contains
the piezoelectric sensor mechanically fixed to the metal strip. In an advantageous
embodiment the device for contactless monitoring of a patient's vital signs is able
to measure the change in position or presence of a patient.
Brief description of drawings
[0015] The measuring mat is shown in figure 1. Figure 2 shows the measuring mat in another
preferred configuration in terms of the arrangement of measuring members. Figure 3
shows the measuring member, including cover. Figure 4 contains a close-up of the circuit
board including piezoelectric sensor. A cross-section through the measuring element
in the position where no force is acting on the measuring element is shown in figure
5, whereas figure 6 shows a cross-section of the measuring element where a perpendicular
force is acting on the cover. Figure 7 shows a close-up of a cross-section of the
measuring element at the place of the piezoelectric sensor. Figure 8 shows a close-up
of a cross-section of the measuring element at the place of the piezoelectric sensor
when a perpendicular force is acting.
Detailed description of drawings
[0016] Fig. 1 and fig. 2 show two different configurations of the measuring mat
1 for contactless measurement of a patient's vital signs. Using this measuring mat
1 it is possible to perform contactless measurement of a patient's vital signs. The
mat
1 can be inserted between the patient support of a bed and the mattress, in an armchair,
a chair or between any backrest and patient's body. The measuring mat
1 may be adapted in both ways by changing its dimensions and the layout of measuring
members
2. One part of the measuring mat
1 is a cable
3 for power supply or signal transmission. This cable
3 may also be adapted for data communication and the measuring mat
1 may also be expanded to include a module for wi-fi, Bluetooth® or other means of
wireless communication for data communication. For easy handling and cleaning the
measuring mat
1 cover is made of flexible waterproof material such as Gore-Tex® textile, plastic
sheeting or other light, waterproof materials.
[0017] Fig. 3 shows a measuring member
2 including a cover
4, supporting
body 5 and metal strip
6 against which a piezoelectric sensor
7 is pressed from below. The metal strip
6 flexes when a vertical force is applied on the cover
4. The supporting body
5 is shaped so that the metal strip
6 fits precisely into part of the supporting
body 5 and also so that there is protection for the main part of the measuring member
2 including the sensor for monitoring slow changes, for example a capacitive sensor
8 and sensor for monitoring rapid changes, for example a piezoelectric sensor
7. The cover
4 presses in several places against the metal strip
6 and in this way it transfers to the metal strip
6 the force applied on it from the surroundings. One part of the measuring member
2 is a cable
3 serving for example for power supply and signal transfer.
[0018] Fig. 4 shows a piezoelectric sensor
7 including a first conductive electrode
9 and a second conductive electrode
10. An piezoelectric element (not in figure) is placed between these conductive electrodes
9,
10. The construction of such piezoelectric sensors
7 is generally known, one example may be the DT Series piezoelectric sensor
7 made by the company Measurement Specialties. The piezoelectric sensor
7 is attached to a circuit board, for example a printed circuit board
12. One part of the printed circuit board
12 is a third conductive electrode
13 near the piezoelectric sensor
7. Along with one of the conductive electrodes
9,
10 of the piezoelectric sensor
7 the third conductive electrode
13 forms a capacitor the parameters of which change depending on the distance between
at least one of the conductive electrodes
9,
10 of the piezoelectric sensor
7 and third conductive electrode
13. First conductor
14, second conductor
15 and third conductor
16 serve to connect the electrodes
9,
10,
13 with the processing unit
17.
[0019] Fig. 5 to fig. 8 show a detailed description of the principle according to the invention.
Fig. 5 shows a cross-section of the measuring member
2 in the first position, where no external force is applied on the cover
4. It shows the cover
4, supporting body
5 of the measuring element, metal strip
6, first rail
18 and second rail
19, which the metal strip
6 is put on. The piezoelectric sensor
7 presses against approximately the centre of the metal strip
6 and is connected at the other end to the circuit board
12. One part of the measuring member
2, as in fig. 5, may be a flexible member
20 which interacts with the piezoelectric sensor
7 via a force in the direction to the metal strip
6. This flexible member
20 may be a spring. In an alternative embodiment the piezoelectric sensor is fixed to
the metal strip
6 and a spring doesn't have to be a part of the measuring member
2.
[0020] Fig. 6 shows a cross-section of the measuring member
2 subjected to a perpendicular force on the cover
4. The transmission of this perpendicular force independent of the place of exerting
occurs via two points of contact between the cover
4 and the metal strip
6. So the applying of a perpendicular force on the cover
4 is expressed by a deflection of the metal strip
6 at a place near the piezoelectric sensor
7 from its original position. The fact that the technical arrangement of the metal
strip
6, cover
4 and supporting body
5 is approximately symmetrical means that the same perpendicular force can act anywhere
on the entire surface of the cover
4 and it is expressed as the same deflection of the metal strip
6.
[0021] Fig. 7 and fig. 8 show how the action of a perpendicular force is expressed on a
piezoelectric sensor
7 itself. Fig. 7 shows a section of the central part of the measuring member
2. In fig. 6 the measuring member
2 is shown with the circuit board
12 and with the piezoelectric sensor
7 in the first position where no external force exerts on the cover. Fig. 8 shows this
part of the measuring member
2 with applied perpendicular force on the cover
4. If the perpendicular force acts on the cover
4 the metal strip deflects from its first position in the direction away from the supporting
body
5. Since the piezoelectric sensor
7 is pushed by the flexible member
20 against the metal strip
6, during the deflection of the metal strip
6 the piezoelectric sensor
7 moves with it. The distance between at least one of the conductive electrodes
9,
10 on the piezoelectric sensor
7 and the third conductive electrode
13 increases, which results in a drop in the measured capacity. An ordinary expert skilled
in the art is capable of designing an alternative solution where the application of
a perpendicular force on the cover
4 causes the metal strip
6 to deflect in the direction to the supporting body
5 of the measuring member
2. Hence the distance between at least one of the conductive electrodes
9,
10 on the piezoelectric sensor
7 and the third conductive electrode
13 will decrease and this increases the measured capacity.
[0022] The application of the perpendicular force on the cover
4 causes a deformation of the piezoelectric sensor
7, which generates a voltage between the first conductor
14 and the second conductor
15. This method of measuring reacts to rapidly caused changes, for example, by the patient's
pulse. The deflection of the piezoelectric sensor
7 causes a change in distance between one of the conductive electrodes
9,
10 of the piezoelectric sensor
7 and the third conductive electrode
13 from distance a to distance
b. It results in a change of capacitance of the formed capacitor measured between one
of the conductive electrodes
9,
10 of the piezoelectric sensor and the third conductive electrode
13. This second method of measuring senses with great accuracy small changes caused
by mechanical expressions of the patient's body. Low frequency changes in capacity
correspond, for example, to respiratory rate where a sudden and significant increase
or decrease in capacity may be evaluated as a change of the patient's presence, i.e.,
whether or not the patient is in bed. The region of interest for the evaluation of
the respiratory rate or increase in weight is the frequency spectrum of changes lower
than 1 Hz. A signal with a frequency of 0,2 Hz may be evaluated as the respiratory
rate. In contrast, the region of interest for evaluation of the pulse rate is the
frequency spectrum of changes around 1 Hz and higher, the pulse rate may be detected
up to 10 Hz.
[0023] Based on an appropriate layout of measuring members
2 in the mat
1, the processing unit
17 can give information about the patient's position, and if there is a danger that
the patient will fall out of bed, it can inform the personnel by signalling a risk
of the patient exiting the bed or the patient falling from the bed. This signalling
may be visual, audio or in some other form. The signalling can also have a local or
system scope, where the risk information is sent by the processing unit
17 to a server, from where the information is distributed to remote devices such as
a monitor in a nurse station or a mobile device with which a nurse is equipped. The
stopping of measurement may be another reason why to evaluate the risk of exiting
the bed.
[0024] On the basis of the measurement of slow changes in capacity, in an advantageous embodiment
the processing unit
17 can be configured so that it measures the patient's weight and can give information
about a reduction or increase in the patient's weight in the case of long-term monitoring
[0025] The invention is defined in the appended claims.
1. A device for contactless monitoring of a patient's vital signs including a measuring
member (2) and a processing unit (17), the measuring member (2) including a piezoelectric
sensor (7) formed by a first and a second conductive electrode (9, 10), connected
to the processing unit (17) , and a piezoelectric element, wherein the measuring member
(2) further contains a third conductive electrode (13) near the piezoelectric sensor
(7), which third conductive electrode (13) is also connected to the processing unit
(17) such that said third conductive electrode (13), along with one of the first and
the second conductive electrodes (9, 10), forms a capacitor for measuring a change
in capacitance when the distance between the one of the conductive electrodes (9,
10) of the piezoelectric sensor (7) and the third electrode (13) varies depending
on the perpendicular force on the measuring member (2).
2. The device according to claim 1 characterized in that the change in distance between at least one of the electrodes (9), (10) of the piezoelectric
sensor (7) and the third electrode (13) is proportional to the change in measured
capacitance between at least one of the electrodes (9), (10) and the third electrode
(13), wherein the capacitance is measured by processing unit (17).
3. The device according to claim 2 characterized in that repetitious changes in capacitance correspond to the patient's respiratory rate.
4. The device according to claim 2 characterized in that significant change in capacity of the sensor (8) corresponds to the presence or position
of a patient.
5. The device according to claim 1 characterized in that repetitious changes in voltage generated by the piezoelectric sensor (7) correspond
to the patient's pulse rate.
6. The device according to claim 1 characterized in that the mechanism for transmission of perpendicular force acts on the cover (4) of the
measuring element (2) including a metal strip (6).
7. The device according to claim 6 characterized in that the position of the piezoelectric sensor (7) in terms of the third electrode (13)
is proportional to the mechanical force acting on the metal strip (6).
8. The device according to claim 6 characterized in that the arrangement of the cover (4), metal strip (6) and supporting body (5) is approximately
symmetrical according to at least one plane perpendicular to the longitudinal direction
of the measuring element (2).
9. The device according to claim 1 characterized in that the device contains at least two measuring elements (2).
10. The device according to claim 6 characterized in that the piezoelectric sensor (7) is pushed against the metal strip (6) by flexible member
(20).
11. The device according to claim 6 characterized in that the piezoelectric sensor (7) is firmly fixed to the metal strip (6).
12. A method for contactless monitoring of a patient's vital signs using the device for
contactless monitoring of a patient's vital signs according to claim 1 characterized in that the application of the force results in a change to the distance between at least
one of the conductive electrodes (9), (10) of the piezoelectric sensor (7) and the
third conductive electrode (13) proximate to the piezoelectric sensor (7) which is
proportional to the capacity measured between at least one of the conductive electrodes
(9), (10) and the third conductive electrode (13) by processing unit (17).
1. Eine Einrichtung zur kontaktlosen Überwachung von Vitalfunktionen des Patienten umfassend
ein Messelement (2), eine Prozesseinheit (17), wobei das Messelement (2) einen piezoelektrischen
Sensor (7) umfasst, der von der ersten und von der zweiten Leitelektrode (9), (10)
gebildet wird und der mit der Prozesseinheit (17) verbunden ist, sowie ein piezoelektrisches
Element, dadurch gekennzeichnet, dass das Messelement (2) außerdem eine dritte Leitelektrode (13) umfasst, die in der Nähe
des piezoelektrischen Sensors (7) angebracht wird, wobei diese Leitelektrode (13)
ebenfalls mit der Prozesseinheit (17) in der Weise verbunden ist, dass diese dritte
Leitelektrode (13) mit einer der ersten und zweiten Leitelektroden (9), (10) einen
Kondensator zur Messung von Kapazitätsänderung bildet, wobei sich der Abstand zwischen
einer der Elektroden (9), (10) des piezometrischen Sensors (7) und der dritten Leitelektrode
(13) in Abhängigkeit von der Kraft ändert, die senkrecht zum Messelement (2) wirkt.
2. Eine Einrichtung zur kontaktlosen Überwachung von Vitalfunktionen des Patienten nach
Anspruch 1, dadurch gekennzeichnet, dass die Änderung des Abstands zwischen mindestens einer der ersten und zweiten Leitelektroden
(9), (10) des piezoelektrischen Sensors (7) und der dritten Leitelektrode (13) direkt
proportional zu der gemessenen Kapazität zwischen mindestens einer der ersten und
zweiten Leitelektrode (9), (10) und der dritten Leitelektrode (13) ist, wobei die
Kapazität mit der Prozesseinheit gemessen wird (17).
3. Eine Einrichtung zur kontaktlosen Überwachung von Vitalfunktionen des Patienten nach
Anspruch 2, dadurch gekennzeichnet, dass die sich wiederholenden Änderungen der Kapazität der Atemfrequenz des Patienten entsprechen.
4. Eine Einrichtung zur kontaktlosen Überwachung von Vitalfunktionen des Patienten nach
Anspruch 2, dadurch gekennzeichnet, dass eine wesentliche Änderung der Kapazität des Sensors (8) der Anwesenheit oder der
Position des Patienten entspricht.
5. Eine Einrichtung zur kontaktlosen Überwachung von Vitalfunktionen des Patienten nach
Anspruch 1, dadurch gekennzeichnet, dass die sich wiederholende Spannungsänderungen, die vom piezoelektrischen Sensor (7)
generiert werden, der Herzschlagfrequenz des Patienten entsprechen.
6. Eine Einrichtung zur kontaktlosen Überwachung von Vitalfunktionen des Patienten nach
Anspruch 1, dadurch gekennzeichnet, dass der Mechanismus zur Übertragung der senkrechten Kraft an die Oberfläche des Gehäuses
(4) des Messelements (2), einschl. Klinge (6) wirkt.
7. Eine Einrichtung zur kontaktlosen Überwachung von Vitalfunktionen des Patienten nach
Anspruch 6, dadurch gekennzeichnet, dass die Position des piezoelektrischen Sensors (7) gegenüber der dritten Leitelektrode
(13) direkt proportional zu der mechanischen Kraft ist, die auf die Klinge (6) wirkt.
8. Eine Einrichtung zur kontaktlosen Überwachung von Vitalfunktionen des Patienten nach
Anspruch 6, dadurch gekennzeichnet, dass die Anordnung des Gehäuses (4), der Klinge (6) und des Tragkörpers (5) im wesentlichen
symetrisch zu mindestens einer zur Längstrichtung des Messelements (2) symetrischen
Ebene ist.
9. Eine Einrichtung zur kontaktlosen Überwachung von Vitalfunktionen des Patienten nach
Anspruch 1, dadurch gekennzeichnet, dass die Einrichtung mindestens zwei Messelemente (2) umfasst.
10. Eine Einrichtung zur kontaktlosen Überwachung von Vitalfunktionen des Patienten nach
Anspruch 6, dadurch gekennzeichnet, dass der piezoelektischer Sensor (7) durch ein Federelement (20) an die Klinge (6) gedrückt
wird.
11. Eine Einrichtung zur kontaktlosen Überwachung von Vitalfunktionen des Patienten nach
Anspruch 6, dadurch gekennzeichnet, dass der piezoelektrischer Sensor (7) mit der Klinge (6) fest verbunden ist.
12. Eine Methode zur kontaktlosen Überwachung von Vitalfunktionen des Patienten, bei der
eine Einrichtung zur kontaktlosen Überwachung von Vitalfunktionen des Patienten nach
Anspruch 1 eingesetzt wird, dadurch gekennzeichnet, dass durch Wirkung einer Kraft der Abstand zwischen mindestens einer der ersten und zweiten
Leitelektroden (9), (10) des piezoelektrischen Sensors (7) und der dritten Leitelektrode
(13) geändert wird, wobei diese Änderung direkt proportional zu der von der Prozesseinheit
(17) gemessenen Kapazität zwischen mindestens einer der ersten und zweiten Leitelektrode
(9), (10) und der dritten Leitelektrode (13) ist.
1. Le dispositif de surveillance sans contact des fonctions vitales du patient comprend
un élément de mesure (2) et une unité de traitement (17), l'élément de mesure (2)
comprend un capteur piézoélectrique (7) formé par une première et une seconde électrodes
conductrices (9), (10) et connecté à l'unité de traitement (17) et un élément piézoélectrique
caractérisé en ce que l'élément de mesure (2) comprend en outre une troisième électrode conductrice (13)
située à proximité du capteur piézoélectrique (7), ladite troisième électrode conductrice
(13) étant également connectée à l'unité de traitement (17) de telle sorte que ladite
troisième électrode conductrice (13) forme avec l'une des première et seconde électrodes
conductrices (9), (10) un condensateur pour mesurer le changement de capacité, la
distance entre l'une des électrodes (9), (10) le capteur piézoélectrique (7) et la
troisième électrode conductrice (13) variant en fonction de la force perpendiculaire
à l'élément de mesure (2).
2. Dispositif de surveillance sans contact des fonctions vitales du patient selon la
revendication 1 caractérisé en ce que la variation de la distance entre au moins l'une des première et seconde électrodes
conductrices (9), (10) du capteur piézoélectrique (7) et la troisième électrode conductrice
(13) est directement proportionnelle à la variation de la capacité mesurée entre au
moins l'une des première et seconde électrodes conductrices (9), (10) et la troisième
électrode conductrice (13), où la capacité est mesurée par l'unité de traitement (17).
3. Dispositif de surveillance sans contact des signes vitaux d'un patient selon la revendication
2 caractérisé en ce que les changements récurrents de capacité correspondent à la fréquence respiratoire
du patient.
4. Dispositif de surveillance sans contact des signes vitaux d'un patient selon la revendication
2 caractérisé en qu'une modification significative de la capacité du capteur (8) correspond à la présence
ou à la position du patient.
5. Dispositif de surveillance sans contact des signes vitaux d'un patient selon la revendication
1 caractérisé en ce que les changements de tension répétitifs générés par le capteur piézoélectrique (7)
correspondent à la fréquence cardiaque du patient.
6. Dispositif de surveillance sans contact des signes vitaux d'un patient selon la revendication
1 caractérisé en ce que le mécanisme de transmission de la force perpendiculaire est appliqué sur la surface
du couvercle (4) de l'élément de mesure (2) y compris la plaque (6).
7. Dispositif de surveillance sans contact des signes vitaux d'un patient selon la revendication
6 caractérisé en ce que la position du capteur piézoélectrique (7) par rapport à la troisième électrode conductrice
(13) est directement proportionnelle à la force mécanique agissant sur la plaque (6).
8. Dispositif de surveillance sans contact des signes vitaux d'un patient selon la revendication
6 caractérisé en ce que l'agencement du couvercle (4), de la plaque (6) et du corps de support (5) est approximativement
symétrique selon au moins un plan perpendiculaire à la direction longitudinale de
l'élément de mesure (2).
9. Dispositif de surveillance sans contact des signes vitaux d'un patient selon la revendication
1 caractérisé en ce que le dispositif comprend au moins deux éléments de mesure (2).
10. Dispositif de surveillance sans contact des signes vitaux d'un patient selon la revendication
6 caractérisé en ce que le capteur piézoélectrique (7) est pressé de force contre la plaque (6) par un élément
souple (20).
11. Dispositif de surveillance sans contact des signes vitaux d'un patient selon la revendication
6 caractérisé en ce que le capteur piézoélectrique (7) est fermement relié à la plaque (6).
12. Procédé de surveillance sans contact des signes vitaux d'un patient utilisant un dispositif
de surveillance sans contact des signes vitaux d'un patient selon la revendication
1 caractérisé en ce que l'action de la force modifie la distance entre au moins l'une des première et seconde
électrodes conductrices (9), (10) du capteur piézoélectrique (7) et la troisième électrode
conductrice (13) située à proximité du capteur piézoélectrique (7), qui est directement
proportionnelle à la capacité mesurée par l'unité du processeur (17) entre au moins
l'une des première et seconde électrodes conductrices (9), (10) et la troisième électrode
conductrice (13).